============================================ WARNING: possible recursive locking detected 6.8.0-rc1-syzkaller-00385-g4854cf9c61d0 #0 Not tainted -------------------------------------------- syz-executor.2/29207 is trying to acquire lock: ffff88802f4ae0d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff88802f4ae0d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4452 [inline] ffff88802f4ae0d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: __dev_queue_xmit+0x1ab3/0x3ed0 net/core/dev.c:4347 but task is already holding lock: ffff8880475480d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline] ffff8880475480d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4452 [inline] ffff8880475480d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: sch_direct_xmit+0x333/0xc20 net/sched/sch_generic.c:340 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(_xmit_ETHER#2); lock(_xmit_ETHER#2); *** DEADLOCK *** May be due to missing lock nesting notation 8 locks held by syz-executor.2/29207: #0: ffff8880835780b0 (slock-AF_INET6/1){+.-.}-{2:2}, at: l2tp_xmit_core net/l2tp/l2tp_core.c:1044 [inline] #0: ffff8880835780b0 (slock-AF_INET6/1){+.-.}-{2:2}, at: l2tp_xmit_skb+0x6bc/0x1940 net/l2tp/l2tp_core.c:1109 #1: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline] #1: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline] #1: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: __ip_queue_xmit+0x72/0x1a50 net/ipv4/ip_output.c:470 #2: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline] #2: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline] #2: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: ip_finish_output2+0x364/0x2540 net/ipv4/ip_output.c:228 #3: ffffffff8d1acb80 (rcu_read_lock_bh){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #3: ffffffff8d1acb80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_read_lock_bh include/linux/rcupdate.h:802 [inline] #3: ffffffff8d1acb80 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x244/0x3ed0 net/core/dev.c:4276 #4: ffff888046cec258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: spin_trylock include/linux/spinlock.h:361 [inline] #4: ffff888046cec258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:195 [inline] #4: ffff888046cec258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: qdisc_run_begin include/net/sch_generic.h:192 [inline] #4: ffff888046cec258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3763 [inline] #4: ffff888046cec258 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x108c/0x3ed0 net/core/dev.c:4317 #5: ffff8880475480d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline] #5: ffff8880475480d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: __netif_tx_lock include/linux/netdevice.h:4452 [inline] #5: ffff8880475480d8 (_xmit_ETHER#2){+.-.}-{2:2}, at: sch_direct_xmit+0x333/0xc20 net/sched/sch_generic.c:340 #6: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline] #6: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline] #6: ffffffff8d1acbe0 (rcu_read_lock){....}-{1:2}, at: ip_finish_output2+0x364/0x2540 net/ipv4/ip_output.c:228 #7: ffffffff8d1acb80 (rcu_read_lock_bh){....}-{1:2}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #7: ffffffff8d1acb80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_read_lock_bh include/linux/rcupdate.h:802 [inline] #7: ffffffff8d1acb80 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x244/0x3ed0 net/core/dev.c:4276 stack backtrace: CPU: 0 PID: 29207 Comm: syz-executor.2 Not tainted 6.8.0-rc1-syzkaller-00385-g4854cf9c61d0 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106 check_deadlock kernel/locking/lockdep.c:3062 [inline] validate_chain kernel/locking/lockdep.c:3856 [inline] __lock_acquire+0x210a/0x3b30 kernel/locking/lockdep.c:5137 lock_acquire kernel/locking/lockdep.c:5754 [inline] lock_acquire+0x1ae/0x520 kernel/locking/lockdep.c:5719 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154 spin_lock include/linux/spinlock.h:351 [inline] __netif_tx_lock include/linux/netdevice.h:4452 [inline] __dev_queue_xmit+0x1ab3/0x3ed0 net/core/dev.c:4347 dev_queue_xmit include/linux/netdevice.h:3171 [inline] neigh_resolve_output net/core/neighbour.c:1563 [inline] neigh_resolve_output+0x584/0x8f0 net/core/neighbour.c:1543 neigh_output include/net/neighbour.h:542 [inline] ip_finish_output2+0x82d/0x2540 net/ipv4/ip_output.c:235 __ip_finish_output net/ipv4/ip_output.c:313 [inline] __ip_finish_output+0x38b/0x650 net/ipv4/ip_output.c:295 ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323 NF_HOOK_COND include/linux/netfilter.h:303 [inline] ip_mc_output+0x1dd/0x6a0 net/ipv4/ip_output.c:420 dst_output include/net/dst.h:451 [inline] ip_local_out+0xaf/0x1a0 net/ipv4/ip_output.c:129 iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x1daa/0x33b0 net/ipv4/ip_tunnel.c:831 erspan_xmit+0x51f/0x1bf0 net/ipv4/ip_gre.c:720 __netdev_start_xmit include/linux/netdevice.h:4989 [inline] netdev_start_xmit include/linux/netdevice.h:5003 [inline] xmit_one net/core/dev.c:3547 [inline] dev_hard_start_xmit+0x137/0x6d0 net/core/dev.c:3563 sch_direct_xmit+0x1ac/0xc20 net/sched/sch_generic.c:342 __dev_xmit_skb net/core/dev.c:3776 [inline] __dev_queue_xmit+0x12b0/0x3ed0 net/core/dev.c:4317 dev_queue_xmit include/linux/netdevice.h:3171 [inline] neigh_resolve_output net/core/neighbour.c:1563 [inline] neigh_resolve_output+0x584/0x8f0 net/core/neighbour.c:1543 neigh_output include/net/neighbour.h:542 [inline] ip_finish_output2+0x82d/0x2540 net/ipv4/ip_output.c:235 __ip_finish_output net/ipv4/ip_output.c:313 [inline] __ip_finish_output+0x38b/0x650 net/ipv4/ip_output.c:295 ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323 NF_HOOK_COND include/linux/netfilter.h:303 [inline] ip_mc_output+0x1dd/0x6a0 net/ipv4/ip_output.c:420 dst_output include/net/dst.h:451 [inline] ip_local_out net/ipv4/ip_output.c:129 [inline] __ip_queue_xmit+0x7cb/0x1a50 net/ipv4/ip_output.c:535 l2tp_xmit_queue net/l2tp/l2tp_core.c:1007 [inline] l2tp_xmit_core net/l2tp/l2tp_core.c:1093 [inline] l2tp_xmit_skb+0x93a/0x1940 net/l2tp/l2tp_core.c:1109 pppol2tp_sendmsg+0x3f2/0x5e0 net/l2tp/l2tp_ppp.c:318 sock_sendmsg_nosec net/socket.c:730 [inline] __sock_sendmsg+0xd5/0x180 net/socket.c:745 sock_write_iter+0x29b/0x3d0 net/socket.c:1160 call_write_iter include/linux/fs.h:2085 [inline] new_sync_write fs/read_write.c:497 [inline] vfs_write+0x6d5/0x1100 fs/read_write.c:590 ksys_write+0x1f0/0x250 fs/read_write.c:643 do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline] __do_fast_syscall_32+0x79/0x110 arch/x86/entry/common.c:321 do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:346 entry_SYSENTER_compat_after_hwframe+0x70/0x7a RIP: 0023:0xf7f5d579 Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00 RSP: 002b:00000000f7f585ac EFLAGS: 00000292 ORIG_RAX: 0000000000000004 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020000840 RDX: 0000000000000573 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 ---------------- Code disassembly (best guess), 2 bytes skipped: 0: 10 06 adc %al,(%rsi) 2: 03 74 b4 01 add 0x1(%rsp,%rsi,4),%esi 6: 10 07 adc %al,(%rdi) 8: 03 74 b0 01 add 0x1(%rax,%rsi,4),%esi c: 10 08 adc %cl,(%rax) e: 03 74 d8 01 add 0x1(%rax,%rbx,8),%esi 1e: 00 51 52 add %dl,0x52(%rcx) 21: 55 push %rbp 22: 89 e5 mov %esp,%ebp 24: 0f 34 sysenter 26: cd 80 int $0x80 * 28: 5d pop %rbp <-- trapping instruction 29: 5a pop %rdx 2a: 59 pop %rcx 2b: c3 ret 2c: 90 nop 2d: 90 nop 2e: 90 nop 2f: 90 nop 30: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi 37: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi